The present invention relates to a centrifuge comprising an outer drum, means journalling said drum for rotation about an axis, a hollow rotor mounted coaxially within said drum and defining therewith a separating space, means for supplying a raw material including a liquid phase and a solid phase to said separating space, outlet means for discharging said liquid and solid phases separately from said separating space, a conveyor screw secured externally to said rotor for axially conveying said solid phase towards the associated outlet means, said conveyor screw having at least two continuous helices, at least one interruption in said conveyor screw intermediate the ends thereof, and means for supplying a washing liquid into the separating space through an opening located adjacent said interruption.
German patent specification No. 1,295,494 discloses a centrifuge of this kind, in which the portions of the screw helix adjoining the interruption therein are axially off-set or staggered relative to one another, so that the leading edge (as determined by the rotation of the screw conveyor relative to the drum) of the interruption is located downstream or forwardly (as viewed in the flow direction of the solid phase) of the trailing edge of the interruption. In other words, the interruption is formed substantially as a slit located in a plane including the axis of the drum and the rotor. In this known centrifuge, the solid matter transported by the conveyor screw is subjected to a certain mechanical working in the region of the interruption, resulting in some loosening of the solids which promotes the washing effect of the liquid supplied through the opening in the rotor wall. Due to the interruption in the screw helix, at least the layer of the solids adjacent the active face of the screw loses the contact with the screw face, so that the inner cohesion of the solids is partially broken, and a certain agitation is effected. The loosened and rearranged solid material is subsequently intercepted by the trailing or rearward edge of the slit, and the temporarily interrupted movement of the material towards the outlet is reassumed.